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Message-ID: <7c7fddf5-9d32-415b-a1c4-3b9402e78d72@huaweicloud.com>
Date: Sat, 31 Jan 2026 08:58:40 +0800
From: Chen Ridong <chenridong@...weicloud.com>
To: Waiman Long <longman@...hat.com>, Tejun Heo <tj@...nel.org>,
Johannes Weiner <hannes@...xchg.org>, Michal Koutný
<mkoutny@...e.com>, Ingo Molnar <mingo@...hat.com>,
Peter Zijlstra <peterz@...radead.org>, Juri Lelli <juri.lelli@...hat.com>,
Vincent Guittot <vincent.guittot@...aro.org>,
Steven Rostedt <rostedt@...dmis.org>, Ben Segall <bsegall@...gle.com>,
Mel Gorman <mgorman@...e.de>, Valentin Schneider <vschneid@...hat.com>,
Anna-Maria Behnsen <anna-maria@...utronix.de>,
Frederic Weisbecker <frederic@...nel.org>,
Thomas Gleixner <tglx@...utronix.de>, Shuah Khan <shuah@...nel.org>
Cc: cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-kselftest@...r.kernel.org
Subject: Re: [PATCH/for-next v2 1/2] cgroup/cpuset: Defer
housekeeping_update() call from CPU hotplug to workqueue
On 2026/1/30 23:42, Waiman Long wrote:
> The update_isolation_cpumasks() function can be called either directly
> from regular cpuset control file write with cpuset_full_lock() called
> or via the CPU hotplug path with cpus_write_lock and cpuset_mutex held.
>
> As we are going to enable dynamic update to the nozh_full housekeeping
> cpumask (HK_TYPE_KERNEL_NOISE) soon with the help of CPU hotplug,
> allowing the CPU hotplug path to call into housekeeping_update() directly
> from update_isolation_cpumasks() will likely cause deadlock. So we
> have to defer any call to housekeeping_update() after the CPU hotplug
> operation has finished. This is now done via the workqueue where
> the actual housekeeping_update() call, if needed, will happen after
> cpus_write_lock is released.
>
> We can't use the synchronous task_work API as call from CPU hotplug
> path happen in the per-cpu kthread of the CPU that is being shut down
> or brought up. Because of the asynchronous nature of workqueue, the
> HK_TYPE_DOMAIN housekeeping cpumask will be updated a bit later than the
> "cpuset.cpus.isolated" control file in this case.
>
> Also add a check in test_cpuset_prs.sh and modify some existing
> test cases to confirm that "cpuset.cpus.isolated" and HK_TYPE_DOMAIN
> housekeeping cpumask will both be updated.
>
> Signed-off-by: Waiman Long <longman@...hat.com>
> ---
> kernel/cgroup/cpuset.c | 37 +++++++++++++++++--
> .../selftests/cgroup/test_cpuset_prs.sh | 13 +++++--
> 2 files changed, 44 insertions(+), 6 deletions(-)
>
> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
> index 7b7d12ab1006..0b0eb1df09d5 100644
> --- a/kernel/cgroup/cpuset.c
> +++ b/kernel/cgroup/cpuset.c
> @@ -84,6 +84,9 @@ static cpumask_var_t isolated_cpus;
> */
> static bool isolated_cpus_updating;
>
> +/* Both cpuset_mutex and cpus_read_locked acquired */
> +static bool cpuset_locked;
> +
> /*
> * A flag to force sched domain rebuild at the end of an operation.
> * It can be set in
> @@ -285,10 +288,12 @@ void cpuset_full_lock(void)
> {
> cpus_read_lock();
> mutex_lock(&cpuset_mutex);
> + cpuset_locked = true;
> }
>
> void cpuset_full_unlock(void)
> {
> + cpuset_locked = false;
> mutex_unlock(&cpuset_mutex);
> cpus_read_unlock();
> }
> @@ -1285,6 +1290,16 @@ static bool prstate_housekeeping_conflict(int prstate, struct cpumask *new_cpus)
> return false;
> }
>
> +static void isolcpus_workfn(struct work_struct *work)
> +{
> + cpuset_full_lock();
> + if (isolated_cpus_updating) {
> + WARN_ON_ONCE(housekeeping_update(isolated_cpus) < 0);
> + isolated_cpus_updating = false;
> + }
> + cpuset_full_unlock();
> +}
> +
> /*
> * update_isolation_cpumasks - Update external isolation related CPU masks
> *
> @@ -1293,14 +1308,30 @@ static bool prstate_housekeeping_conflict(int prstate, struct cpumask *new_cpus)
> */
> static void update_isolation_cpumasks(void)
> {
> - int ret;
> + static DECLARE_WORK(isolcpus_work, isolcpus_workfn);
>
> if (!isolated_cpus_updating)
> return;
>
> - ret = housekeeping_update(isolated_cpus);
> - WARN_ON_ONCE(ret < 0);
> + /*
> + * This function can be reached either directly from regular cpuset
> + * control file write (cpuset_locked) or via hotplug (cpus_write_lock
> + * && cpuset_mutex held). In the later case, we defer the
> + * housekeeping_update() call to the system_unbound_wq to avoid the
> + * possibility of deadlock. This also means that there will be a short
> + * period of time where HK_TYPE_DOMAIN housekeeping cpumask will lag
> + * behind isolated_cpus.
> + */
> + if (!cpuset_locked) {
Adding a global variable makes this difficult to handle, especially in
concurrent scenarios, since we could read it outside of a critical region.
I suggest removing cpuset_locked and adding async_update_isolation_cpumasks
instead, which can indicate to the caller it should call without holding the
full lock.
> + /*
> + * We rely on WORK_STRUCT_PENDING_BIT to not requeue a work
> + * item that is still pending.
> + */
> + queue_work(system_unbound_wq, &isolcpus_work);
> + return;
> + }
>
> + WARN_ON_ONCE(housekeeping_update(isolated_cpus) < 0);
> isolated_cpus_updating = false;
> }
>
> diff --git a/tools/testing/selftests/cgroup/test_cpuset_prs.sh b/tools/testing/selftests/cgroup/test_cpuset_prs.sh
> index 5dff3ad53867..0502b156582b 100755
> --- a/tools/testing/selftests/cgroup/test_cpuset_prs.sh
> +++ b/tools/testing/selftests/cgroup/test_cpuset_prs.sh
> @@ -245,8 +245,9 @@ TEST_MATRIX=(
> "C2-3:P1:S+ C3:P2 . . O2=0 O2=1 . . 0 A1:2|A2:3 A1:P1|A2:P2"
> "C2-3:P1:S+ C3:P1 . . O2=0 . . . 0 A1:|A2:3 A1:P1|A2:P1"
> "C2-3:P1:S+ C3:P1 . . O3=0 . . . 0 A1:2|A2: A1:P1|A2:P1"
> - "C2-3:P1:S+ C3:P1 . . T:O2=0 . . . 0 A1:3|A2:3 A1:P1|A2:P-1"
> - "C2-3:P1:S+ C3:P1 . . . T:O3=0 . . 0 A1:2|A2:2 A1:P1|A2:P-1"
> + "C2-3:P1:S+ C3:P2 . . T:O2=0 . . . 0 A1:3|A2:3 A1:P1|A2:P-2"
> + "C1-3:P1:S+ C3:P2 . . . T:O3=0 . . 0 A1:1-2|A2:1-2 A1:P1|A2:P-2 3|"
> + "C1-3:P1:S+ C3:P2 . . . T:O3=0 O3=1 . 0 A1:1-2|A2:3 A1:P1|A2:P2 3"
> "$SETUP_A123_PARTITIONS . O1=0 . . . 0 A1:|A2:2|A3:3 A1:P1|A2:P1|A3:P1"
> "$SETUP_A123_PARTITIONS . O2=0 . . . 0 A1:1|A2:|A3:3 A1:P1|A2:P1|A3:P1"
> "$SETUP_A123_PARTITIONS . O3=0 . . . 0 A1:1|A2:2|A3: A1:P1|A2:P1|A3:P1"
> @@ -764,7 +765,7 @@ check_cgroup_states()
> # only CPUs in isolated partitions as well as those that are isolated at
> # boot time.
> #
> -# $1 - expected isolated cpu list(s) <isolcpus1>{,<isolcpus2>}
> +# $1 - expected isolated cpu list(s) <isolcpus1>{|<isolcpus2>}
> # <isolcpus1> - expected sched/domains value
> # <isolcpus2> - cpuset.cpus.isolated value = <isolcpus1> if not defined
> #
> @@ -773,6 +774,7 @@ check_isolcpus()
> EXPECTED_ISOLCPUS=$1
> ISCPUS=${CGROUP2}/cpuset.cpus.isolated
> ISOLCPUS=$(cat $ISCPUS)
> + HKICPUS=$(cat /sys/devices/system/cpu/isolated)
> LASTISOLCPU=
> SCHED_DOMAINS=/sys/kernel/debug/sched/domains
> if [[ $EXPECTED_ISOLCPUS = . ]]
> @@ -810,6 +812,11 @@ check_isolcpus()
> ISOLCPUS=
> EXPECTED_ISOLCPUS=$EXPECTED_SDOMAIN
>
> + #
> + # The inverse of HK_TYPE_DOMAIN cpumask in $HKICPUS should match $ISOLCPUS
> + #
> + [[ "$ISOLCPUS" != "$HKICPUS" ]] && return 1
> +
> #
> # Use the sched domain in debugfs to check isolated CPUs, if available
> #
--
Best regards,
Ridong
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